The invention relates to the production of alkyl tert alkyl ethers and, specifically, to a process for producing tert amyl methyl ether (TAME) from a feedstock containing relatively high amounts of diolefin such as a light naphtha stream from a coker refinery facility.
Alkyl tert alkyl ethers are useful as fuel extenders and octane value improving agents in the production of unleaded gasoline. These ether additives are particularly useful as environmentally more acceptable substitutes for lead anti-knock compounds.
Of these ether additives, tert amyl methyl ether (TAME) is presently probably the most important oxygenate after methyl tert butyl ether (MTBE) and ethanol. TAME is produced from C.sub.5 feedstocks from various refineries and petrochemical facilities. These feedstocks are a good source of isoamylene and are generally readily available, thereby rendering TAME further attractive economically. Additionally, TAME provides a reasonably good octane number while yielding a blend with a low RVP.
Main sources of isoamylene for TAME production include catalytic and steam cracker units. However, other feedstocks also provide a good supply of isoamylene. One such feedstock is a light naphtha cut from a typical coker unit. This feedstock has a similar amount of isoamylene to the aforementioned FCC and steam cracker C.sub.5 cuts, but is generally worthless due to the relatively large degree of contaminants contained therein in the form of diolefins in the range of 5-6% wt, nitrogen compounds in the order of about 30 ppm and sulfur compounds in the range of about 2000 ppm or greater. Each of these contaminants tends to rapidly deactivate the etherification catalyst. In this regard, methods have been derived for negating the effects of the nitrogen compounds (see U.S. Pat. No. 5,238,541 to Marquez et al.) and sulfur (co-pending and commonly assigned U.S. patent application Ser. No. 08/128,383). However, no process has been provided for negating the adverse effect of diolefins and, accordingly, light coker naphtha feedstocks are not valued as etherification starting feedstocks.
It is therefore the primary object of the invention to provide a process for preparing alkyl tert alkyl ether from a feedstock having a relatively high level of diolefin wherein the catalyst is not poisoned.
It is a further object of the present invention to provide a process whereby TAME can be produced in an efficient, versatile and cost effective manner.
Other objects and advantages will appear hereinbelow.